Frequency of herpes simplex virus-specific cytotoxic T lymphocyte precursors in lymph node cells of infected mice.

The limiting dilution technique was used to estimate the frequency of cytotoxic T lymphocyte precursors (CTL-P) specific to herpes simplex virus (HSV)-infected syngeneic cells in draining lymph nodes from CBA mice infected 5 days previously with HSV. Significant numbers of virus specific CTL-P were found with infected mice whereas such cells were usually undetectable in uninfected mice. On the basis of MHC restriction and Lyt phenotype, the cells were identified as T lymphocytes. Two subsets of HSV-specific CTL-P could be defined; an infrequent one (1/12,500-1/30,000) which grew in the presence of growth promoting factors present in concanavalin A-conditioned medium, and a frequent population (f = 1/1200-1/4750) which in addition required exposure to antigen. In some experiments, the frequent subset of HSV-specific CTL-P was only detectable at low cell number inputs. Similar results in other systems have been explained by active suppression.